In a motor driving control system used to a DC brushless motor, there are widely used two systems of a sensor driving system which uses a position sensor such as a hall sensor and a sensorless driving system which generates rotor position information from an induced voltage generated in a motor coil. A motor drive control device not provided with the position sensor generates a phase signal (pulse signal) by comparing between the induced voltage which emerges at the motor terminal in an open section (non-energization phase) and a reference voltage (equivalent neutral point electrical potential) with a comparator, and detects a rotational position of the rotor based on the phase signal.
A motor driving device is disclosed in JP-A-2008-301550 which outputs a drive selection signal for activating a motor by sensor driving and switching the motor to sensorless driving when the number of revolutions increases, and in which a drive switching unit continues the sensor driving even after the sensorless driving is selected and switches the excitation sequence to the sensorless drive while avoiding a shift period defined between an edge of the sensor signal and an edge of a zero-cross signal to be used as a reference instead of the edge of the sensor signal.